The heart

The 2 halves of the heart are separated by a muscular wall called the septum

The heart is divided into 4 chambers – 2 on the left and 2 on the right

The top chambers are called the left and right atria – atria is plural for atrium

The bottom chambers are called the left and right ventricles

There are 4 valves in the heart which stop blood flowing back when it has been squeezed into the next chamber or blood vessel.

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Blood Flow

Blood enters the right side of the heart through the superior (SVC) and inferior vena cava (IVC)

The SVC brings de-oxygenated blood from the upper part of the body

The IVC brings de-oxygenated blood from the lower part of the body

The SVC & IVC deliver blood into the 1st of the 4 chambers of the heart, the right atrium.

When the right atrium is full it contracts and blood is pushed through the tricuspid valve into the 2nd chamber of the heart – the right ventricle. When the right ventricle is full, blood is pumped through the pulmonary valve into the pulmonary artery which carries blood to the lungs where it becomes oxygenated. The pulmonary artery is the only artery to carry de-oxygenated blood. Once the blood has been oxygenated in thelungs it comes back to the heart via the pulmonary vein (this is the only vein to carry oxygenated blood). The pulmonary vein brings the oxygenated blood to the 3rd chamber of the heart – the left atrium, through the mitral valve. When the right atrium is full it contracts and pumps the blood through the aortic valve out of the heart via the aorta. The aorta splits off into many different blood vessels which carry oxygenated blood all over the body. The left ventricle has the thickest muscle of all of the heart chambers because it has to pump blood to the rest of the body.

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Summary of blood flow

Superior and inferior vena cava

Into right atrium

Through the tricuspid valve

To the right ventricle

Through the pulmonic valve

To the pulmonary arteriesto the lungs

The blood picks up oxygen in the lungs

Then flows from the lungs

To the pulmonary veins

To the left atrium

Through the mitral valve

To the left ventricle

Through the aortic valve

To the aorta

To the body

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Important info about blood flow

You need to know the journey blood takes through the heart but you MUST remember that blood enters the right and left atria from the vena cavae & pulmonary vein at the same time.

This blood is then squeezed into the left and right ventricles at the same time.

And then squeezed into the aorta & pulmonary artery at the same time.

Our heartbeat is the contraction & relaxation of the atria and then the contraction & relaxation of the ventricles – which means that the L&R atria contract at the same time& the L&R ventricles contract at the same time.

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ECG

An ECG records the rhythms and electrical activity of your heart.

A number of electrodes (small metallic discs) are placed on your arms, legs and chest. The electrodes are connected to a machine that records the electrical signals of each heartbeat.

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The Cardiac Cycle

The cardiac cycle is what happens when the atria and ventricles of the heart contract and relax during a heartbeat.

Electrical impulses start at the SA (Sino Atrial) node in the right atrium and are then transmitted across the heart setting off the chain of events that form the cardiac cycle. The SA node is the heart’s natural pacemaker.

Each part of the cardiac cycle can be seen in a ECG.

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PQRST wave

P wave is when the L&R atria contract and blood is pushed into the L&R ventricles

The L&R ventricles are filling with blood between the P and Q waves

Q wave is when the electrical signal tells your L&R ventricles to contract

R wave is when the right ventricle contracts

S wave is when the left ventricle contracts

T wave is when the walls of the L&R ventricles are relaxing

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Blood Pressure

Blood pressure is the pressure of the blood in your arteries. You need a certain amount of pressure in your arteries to keep the blood flowing around your body.

The pressure of blood flowing through the arteries varies at different times in the heartbeat cycle.

Systolic blood pressure is the highest level your blood pressure reaches. This is when your heart contracts and blood is forced through the arteries.

Diastolic blood pressure is the lowest level your blood pressure reaches. This is when your heart relaxes between each beat.

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Measuring Blood Pressure

Your blood pressure is expressed as two numbers – for example, 120/80mmHg. (‘mmHg’ is the unit used for measuring blood pressure. It stands for millimetres of mercury.)

The first number is the systolic pressure (when the heart is contracting) and the second is the diastolic pressure (when the heart is relaxing). According to the BHF the target for the general population is to have a blood pressurebelow140/90mmHg.

Blood pressure is measured using a sphygmomanometer.

When you have your BP taken - the cuff is inflated until it stops blood passing through the brachial artery in your arm. At this point there will be no pulse.

The cuff is then slowly deflated until the pulse is felt – this is the systolic pressure. The cuff continues to deflate until the sound of the pulse fades – this is the diastolic pressure.

In general high blood pressure (or hypertension) is more of a health problem than low blood pressure (hypotension). High blood pressure is caused by hardening of the arteries caused by a loss of elasticity in the arteries. Many things contribute to this loss of elasticity.

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Pulse

Your pulse is the wave of your heart contracting as it pumps blood out.

Heart rate = the no. of times your heart beats in a minute

Most adults have a resting heart rate of 72-80 bpm.

To work out your heart rate find your pulse, count the number of beats for 10 seconds then x that no. by 6.

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Arteries

Have narrow lumen

Have thick, highly muscular walls (except for the arteries of the cranium and vertebral column)

Carry oxygenated blood (exception= the pulmonary artery which carries de-oxygenated blood from the heart to the lungs)

Carry blood away from the heart

Do not have valves

Blood in them moves under higher pressure and has a pulse

Arteries branch into smaller arterioles

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Veins

Have wide/large lumen

Have thinner walls

Carry de-oxygenated blood (exception=the pulmonary vein which carries oxygenated blood from the lungs to the heart)

Carry blood to the heart

Have valves to prevent the back-flow of blood

Blood in them moves under very low pressure and does not have a pulse

Veins branch into smaller venules

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Capillaries

These are the smallest blood vessels and the walls are only 1 cell thick.

This means that nutrients and oxygen can diffuse OUT through the walls of the capillaries to surrounding cells and carbon dioxide and other waste products can diffuse IN from the surrounding cells into the capillaries and then taken away to be excreted

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Red Blood Cells

These blood cells are formed in the red bone marrow and contain haemoglobin. They live for approx. 120 days

Haemoglobin is an iron rich protein which picks up oxygen as the cells pass through the lungs

These blood cells transport oxygen around the body and release it to organs and tissues throughout the body

They have a bi-concave shape which gives them a large surface area which means they can pick up more oxygen

They are broken down in the spleen & then the liver where any spare iron is retrieved & recycled

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Platelets

These blood cells help

prevent abnormal or excessive bleeding by forming clots .They are formed in the bone marrow from parts that break off large cells

They activate the clotting process in the presence of air and

foreign material

They aretiny, very fragile & irregularly shaped.They need to be fragile as they need to break to release thromboplastin which starts the clotting reaction

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White Blood Cells

These blood cells play a major role in defending the body against disease producing bacteria, viruses and fungi

They are irregularly shaped and produced in the bone marrow. Their life span ranges from hours to years depending on the type of cell

There are three main types of leukocytes, & each type performs a specific infection-fighting function

Monocytes – defend against bacterial infection

Granulocytes – there are several different types of these. They defend the body by rapidly increasing in number and engulfing & destroying foreign substances

Lymphocytes - consist of two types of cells which work together to create a complex interaction to regulate the immune response.

T cells attack virus-infected and malignant cells.

B cells produce and release antibodies, or protein

substances, which bind to infectious agents and help prevent them from doing damage to the body